Arteriosclerosis indicates a state in which arteries are thickened and hardened, leading to various pathological conditions. If narrowing of blood vessels occurs as arteriosclerosis becomes worse, the flow of blood in the arteries may be blocked, possibly causing fatal diseases such as cerebral infarction and myocardial infarction as oxygen and nutrients cannot reach critical tissues. In the case of arteriosclerosis, if artery walls become weakened due to atherosclerosis associated with large amounts of lipid deposition, vessel walls are expanded due to blood pressure, causing aneurysm. Rupture of aneurysm also can kill organisms.
If vascular diseases, such as arteriosclerosis, narrowing of blood vessels, and aneurysm, can be discovered at an early stage, it is possible to prevent fatal diseases, such as cerebral infarction and rupture of aneurysm, from occurring. In particular, aneurysm surgery is risky. Therefore, it is desirable that blood vessels be preserved as long as possible, and aneurysm be removed at a safe stage by surgery. Accordingly, noninvasive diagnosis is preferred for vascular diseases overall.
As a noninvasive diagnosis method for vascular diseases, the following methods are known. PWV is a method of evaluating the stiffness of blood vessels by measuring elastic-wave propagation speeds of the blood vessels (Refer to “Womersley J R: Oscillatory motion of a viscous liquid in a thin-walled elastic tube, I: The linear approximation for long waves. Phil Mag, 1955; 46:199-221” as Non-Patent Document 1; the contents of Non-Patent Document 1 are incorporated herein by reference.). IMT is a method of observing the shapes of vessel walls through imaging of blood vessels by ultrasonic waves (Refer to “Pignoli P, et al: Intimal plus medical thickness of the arterial wall: A direct measurement with ultrasound imaging. Circulation, 1986; 74: 1399-1406” as Non-Patent Document 2; the contents of Non-Patent Document 2 are incorporated herein by reference.). ABI is a method of examining blood-flow resistance by measuring a difference in blood pressure between two points (Refer to “Weiltz J I: Diagnosis and treatment of chronic arterial insufficiency of lower extremities, a critical review, AHA Medical/Scientific Sttements, 1996” as Non-Patent Document 3; the contents of Non-Patent Document 3 are incorporated herein by reference.).